This invention relates to the production of optical fiber ribbons and bundles (Lightpack(copyright)) and, more particularly, to that portion of the production line commonly referred to as the buffering or extrusion line.
Optical fibers possess signal transmission capabilities which vastly exceed those of metallic conductors and, as a consequence, the communications industry relies more and more on optical fibers for such transmissions. Despite the advantages to be realized with optical fibers, they possess inherent disadvantages which must be overcome in order for their full potential to be realized.
For example, optical fibers are quite brittle and can break if bent too sharply or are even subject to small elongations due to tensile stress. Furthermore, even where stresses are not sufficient to cause breakage, they can cause increases in optical attenuation. In addition, splicing individual fibers can present other problems leading to decreased transmission capability or increased signal loss. It is generally preferable to handle and splice fibers in groups rather than individually, and, as a consequence, they are often grouped together in the form of a bundle of fibers or disposed side by side in a matrix material to form a ribbon. Cabling can then comprise stacking a plurality of ribbons, as is shown in U.S. Pat. No. 4,129,469 of Knab, or combining several bundles into a larger bundle.
In U.S. Pat. No. 4,289,558 there is shown as arrangement for assembling a plurality of fibers into a ribbon configuration. A plurality of rotatable fiber spools, each containing an individual fiber wound thereon, supply fiber to a series of sheaves which orient the fibers pulled off of the rotating spools into a side by side configuration which then proceed through an alignment stage including one or more fiber organizers and then into a laminating apparatus where the matrix material is applied to form the multi-fiber ribbon. The ribbon is then wound on a take-up spool. Throughout the entire process, the fibers are maintained under tension which, among other things, causes the supply spools to rotate as the fiber is pulled therefrom. The use of rotating supply reels, especially when the fiber is pulled therefrom, has several disadvantages. First and perhaps foremost, is that the fiber is under tension, hence, careful monitoring of the tension is necessary to prevent fiber breakage. Secondly, it is necessary to have a braking or clutch arrangement to govern the speed of rotation of the supply spools, which can cause further possibly deleterious increases in tension on the fiber. Thirdly, tie-ins must be made at relatively slow speeds of rotation of the supply spools. A tie-in is simply when a second fiber is inserted into the extruder to continue the manufacturing process when the first fiber reaches its end. Also, slowing down the speed of rotation of the supply spools also requires a modification of the extruder to insure uniform application of, for example, the matrix material. Finally, the use of rotating spools prevents measuring the transmission characteristics of the fiber during pay-out.
To overcome the problems resulting from fiber tension and rotating supply spools, over-the-spool-end pay-out (OTE) has been used. In over-the-end pay-out, the supply spool is stationary and the fiber flies off of one end thereof, under near zero tension. As a consequence, the inertia of the spool is eliminated and no braking or clutching thereof is required, thus rapid start up and shut down of the fiber pay-out is made possible. In addition, the speed range is quite broad, from, for example, zero to twenty meters per second (0-20 m/sec). Inasmuch as the spool is non-rotating, the inside end of the fiber can be used for continuously testing the transmission characteristics of the fiber such as with an optical time domain reflectometer (OTDR) attached to the inside, non-moving, fiber end. There is virtually no pull-back tension on the spool, and rotating shafts and spindles are eliminated, materially contributing to the simplicity of the fiber pay-out system.
Despite these numerous advantages of the OTE pay-out, there is a problem inherent to the arrangement, and that is there exists a tendency to impart a twist to the fiber between the spool and the remainder of the system. This twist can accumulate to where the fiber can become badly tangled, even to the extent that the fiber might break or the system must be shut down to remove the tangle. It can be appreciated that where a large number of supply spools is involved, this can become an extremely serious problem.
The present invention is directed to the substantial, if not complete, nullification of this twist so that accumulation thereof and consequent fiber entanglement is eliminated.
The present invention comprises a means for passing the coated fiber emerging from the spool in over-the-end pay-out through a capstan and belt arrangement wherein the belt maintains the fiber in contact with the surface of the capstan. A means is provided for positioning the fiber on the surface of the capstan in a manner such that as the fiber and the sheave member or capstan move through at least a partial revolution of the sheave member, a twist is imparted to the fiber which counteracts the twist therein imparted by the OTE pay-out. As a consequence, the fiber between the supply spool and the capstan has virtually no twist and tangling is substantially completely eliminated.
In greater detail, the invention comprises, in a preferred embodiment thereof, a module located at a focal point of each supply spool. The module comprises a platform upon which a freely rotatable sheave member is mounted. First and second rotatable idler sheaves are mounted in fixed position on the platform, and a third idler sheave is mounted on the distal end of a movable arm, the proximal end of which is pivotally mounted to the axis of one of the idler sheaves. A flat endless belt is disposed about the idler sheaves in a manner such that it bears against at least a portion of the surface of the sheave member. The movable or pivotable arm is spring loaded so that it maintains sufficient belt tension to maintain, in turn, the belt in firm contact with the surface of the sheave member. Fiber from the supply spool is passed through a guide nozzle mounted in a stanchion which, in turn, is mounted on the platform adjacent the sheave member. The guide nozzle is positioned to guide the fiber onto the surface of the sheave member so that it is positioned between the surface of the sheave member and the surface of the belt which bears against that surface, and is maintained in contact with both the surface and the belt through at least a portion of their length.
In accordance with a feature of the invention, the height of the axis of the nozzle, and hence, the vertical position of its exit end relative to the surface of the sheave member, which is vertically oriented, is made adjustable by means for raising or lowering the stanchion relation to the base. The means for raising the stanchion, in its simplified form, comprises one or more shims, which afford a simple and quick means for achieving extremely accurate positioning of the height of the nozzle relative to the base, and hence, relative to the surface of the sheave means or capstan. Alternative means, such as, for example, a camming arrangement, might readily be used to move the stanchion or, alternatively, the nozzle may be mounted in the stanchion in such a manner that it might be moved up or down, as desired.
In operation, the fiber exiting the module is under tension from further apparatus downstream, and, hence, as the fiber is pulled through the module, the sheave member rotates and the belt also is caused to move. However, between the supply spool and the entrance to the module, i.e., the nozzle, there is very little tension inasmuch as the fiber pays out freely, and with no force such as a brake, from the spool. As was pointed out hereinbefore, the OTE pay-out imparts a twist to the fiber over this distance. It has been found that when the fiber on the surface of the sheave member is off center relative to the belt, the belt imparts a twist to the fiber which, depending upon how far off center the fiber is, effectively counteracts the twist in the fiber coming from the supply spool. As a consequence, when the degree of nozzle offset is correct, there is little or no twist in the fiber between the supply spool and the nozzle, and the threat or possibility of twist accumulation and consequent entanglement, is effectively eliminated.
An adjustable belt tensioner functions to insure that the belt, during operation, bears against the surface of the sheave member to insure proper interaction between the belt and the fiber.
These and other features and advantages of the present invention will be more readily apparent from the following detailed description, read in conjunction with the accompanying drawings.